Wear-saving contact structure for rotors of counting devices and the like



R. E. WEAR-SAVING CONTACT STRUCTURE FOR ROTORS June 5, 1956 BROWN OF COUNTING DEVICES AND THE LIKE 2 Sheets-Sheet 1 Filed Nov, 21, 1952 MN NW RALPH E. BROWN INVENTOR.

ATTORNFK June 5. 1956 E. BROWN 2,749,397

R WEAR-SAVING CONTACT STRUCTURE FOR ROTORS OF COUNTING DEVICES AND THE LIKE Filed Nov. 21, 1952 2 Sheets-Sheet 2 "PATH OF CON7I4C734 RALPH E. BROWN,

INVENTOR.

A TTORNEK United States Patent WEAR-SAVIN G CGNTACT STRUCTURE FOR ROTORS OF COUNTING DEVICES AND THE LIKE Ralph E. Brown, Los Angeles, Calif., assignor to Dougias Aircraft Company, Inc., Santa Monica, Calif.

Application November 21, 1952, Serial No. 321,800

9 Claims. (Cl. 200-46) This invention relates to contact means mounted on a rotor for cooperation with fixed contact means carried by a surrounding stator and is concerned with the problem of wear arising from friction between the rotary contact means and the fixed contact means. Usually adjacent surfaces of the stator are also involved. Such wear arises from the fact that the rotor contact means is normally yieldingly pressed outward against the stator and the outward pressure is greatly augmented by centrifugal force acting on the rotor contact means during high speed operation of the rotor.

The basic concept underlying the invention is to provide auxiliary centrifugal means to oppose the centrifugal force that acts on the rotor contact. In some practices of the invention the opposing centrifugal means merely compensates to a desirable degree for the centrifugal force that acts directly on the rotor contact, the arrangement being such that the compensating force does not completely overcome the tendency of the rotor contact to press outward against the stator structure during high speed operation. In such instances the function of the auxiliary centrifugal means is merely to modify the centrifugal tendency of the rotor contact to press outward and the net result in response to progressively increasing speed of rotation may be progressive increases in the outward pressure exerted by the rotor contact or progressive decrease or, in some instances, substantially no change in the outward pressure.

In other practices of the invention where the rotor contact means need touch the stator contact means only when the rotor is stationary or is turning at a relatively slow speed, the auxiliary centrifugal means is adapted to completely overcome the tendency of the rotor contact means to press outward under high speed conditions. In such practices of the invention the auxiliary centrifugal means actually withdraws the rotor contact means inward away from the stator to eliminate frictional wear completely during high speed operation of the device.

This basic concept is carried out by mounting the rotor contact in a radially movable manner with a normal yielding tendency to move outward toward the stator and by equipping the rotor with centrifugal weight means operatively connected with the rotor contact in such manner that outward centrifugal response of the weight means exerts inwardly directed force on the rotor contact. The counteracting centrifugal weight means may take various forms and may be operatively connected to the rotor contact means in various ways.

A feature of the preferred practice of the invention is the use of a bowed leaf spring for the dual purpose of urging the rotor contact outward and of operatively connecting the rotor contact with the auxiliary centrifugal means. In such an arrangement the auxiliary centrifugal means is so connected to the leaf spring as to tend to reduce the curvature of the leaf spring in the region of the rotor contact in response to rotation of the rotor. A further feature of the preferred practice of the invention 2,749,397 Patented June 5, 1956 is the use of the same leaf spring to normally urge the auxiliary centrifugal means inward. A still further feature in the preferred practice of the invention is the use of the leaf spring to connect the rotor contact means into a circuit.

While the invention is broadly applicable for its purpose to various rotary devices of the type in which a rotor contact cooperates with fixed contact means, the invention has been initially embodied in a computing device constructed to serve as an analog digital converter. For the purpose of disclosure and to illustrate the principles involved, such an embodiment of the invention will be described herein. It will be apparent that this description will provide adequate guidance for those skilled in the art who may have occasion to apply the same principles to other specific purposes.

The features, advantage and utility of the invention may be readily understood from this description in conjunction with the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative,

Figure 1 is a longitudinal, sectional view taken along the axis of a computing device incorporating the inventron;

Figure 2 is a transverse section taken on the line 2-2 of Figure 1, portions being broken away to reveal the structure;

Figure 3 is a wiring diagram showing the relation between a rotor contact and a circular series of stator contacts;

Figure 4 is a transverse section taken on the line 4-4 of Figure 1;

Figure 5 is an end view of the rotor, portions being broken away to reveal the structure;

Figure 6 is a perspective view of an assembly comprising a rotor contact, a leaf spring, and two centrifugal weights;

Figure 7 is a fragmentary sectional view illustrating one stage in the mounting of the rotor contact on the leaf spring;

Figure 8 is a similar view showing the construction after the mounting operation is completed; and

Figure 9 is a diagrammatic development of the interior surface of one of the stators in the device.

The drawings show a counting device which is described in detail in my copending application entitled Counting Device, Ser. No. 209,427, filed on or about February 5, 1951, which copending application now Patent Number 2,620,980 is hereby made a part of the present disclosure by reference.

Figure 1 shows the construction of an assembly or bank of counters or commutation units, which bank comprises a unit counter, generally designated 20, a lOs counter, generally designated 21, and a l00s counter, generally designated 22, these three counters being actuated by an input shaft 25. The input shaft 25 may be termed a master member since it rotates in accord with the changing values of a variable that is to be computed and by its rotation imposes those values on the counter assembly.

Each of the three counters 20, 21, and 22 has a rotor 23 surrounded by a stator 24, the rotor being mounted on a shaft 31. Each stator 24 carries four fixed circumferential contact means to operate with four corresponding contact means carried by the rotor. Thus each stator 24, which is of non-conducting material, has a circular series of ten conducting segments or fixed contacts, generally designated 26, for controlling a recording system and a duplicate circular series of ten segments or contacts, generally designated 27, for controlling a visible signal system. Each rotor 23 has a contact 29 to sweep the series of segments 26 and a second contact 30 to sweep the second series of segments 27. Each rotor 23 also carries a third contact 32 that sweeps a fixed continuous contact or contact ring 33 of the stator and a fourth contact 34 that cooperates with three fixed stator segments 35, 36, and 37.

It is contemplated that in each instance where there is a series of fixed circumferential contacts or segments of contacts, as in the series of stator segments 26, the series of stator segments 27 and series of three stator segments 35, 36, and 37, the succeeding contacts in each series will be insulated from each other but will have ends that overlap in the direction of circumferential progression around the stator. The stator contacts overlap in this manner to permit the corresponding rotor contacts to shift in a lateral or axial direction with snap action from one contact to another, this lateral snap or jump action being caused by special magnetic means to prevent any possibility of a rotor contact stopping in a dead space on the stator. Thus, in the course of one rotation of the rotor 2 each of the four rotor contacts 29, 3%, and 3 d ten circumferential advances and ten alternate lateral movements as may be understood by reference to the dotted lines in Figure 9. It will be noted that the lateral movements alternate in direction.

To permit the four rotor contacts 2), 3 3-, 32, and 34 to make the lateral movements indicated in Figure 9, the shaft that carries the rotor in each counter is mounted for lim ted longitudinal or axial reciprocation in addition to to tron and reciprocates longitudinally in response to energization of a solenoid coil dtl.

Energization of the solenoid coil 5% in the units counter 26 is controlled by a special set of il stator segments or contacts ll; in cooperation with a rotor contact 42, but each of the solenoid coils it) in the higher order counters and is controlled. by the contact 34 and the associated segments 35, 3e and 37 in the next lower counter. Thus the Contact 34- (not shown) in the unit counter 29, cooperating with the associated segments 35, 36, and 3? (not shown) controls the solenoid coil 40 (not shown) in the lOs c r er 21, and the contact 34 (not shown) in the lOs coun -r 21, cooperating with the associated segments 35, 36 and 3'7 controls the solenoid coil as in the 100 s counter 22.

The input shaft or master member 25 drives mechanism to cause relative rotation between the rotor contact 42 and the ten special segments or stator contacts ll and is also directly connected to the shaft 31 of the units counter 29 to cause the first shaft 31 in the series to rotate synchronously with the input shaft. The shaft 31 of he units co T2161 29 is opcratively connected to the shaft 33. of the lOs counter 2i by a series or" four gears 43, 44, 45, and 46 to rotate the second shaft 3i at onetenth the speed of the first. shaft l-l, since the proposed computation is to be based on the decimal system with the rotation of counter divided into ten parts. In like manner the second shaft 31 the second counter 2i. is Conn ted to the third shaft 31 in the third counter 22 by a similar set of gears 43-46 (not shown) to rotate the third shaft in the hundrcds counter at one-tenth the rate of the see id shaft in tl e tens counter.

One side of each of the three solenoid coils Alt} is connected to the positive or hot side of a suitable source current. The negative or grounded side of the source of c1" "1! (.QrzfiCC l to the casing or ground of the ounts asseholy. second side of the first coil 40 in the units counter 20 is electrically connected to the ten special stator contacts 41 as indicated in the small wiring diagram in Figure 3, the circuit being completed by grounding the rotor contact 42. The second side of the electronagnetic coil (not shown) in the s counter 21 is electrically connected to the segment 36 in the unit counter and in like manner the second side of the third electro-rnagnetic coil (not shown) in the 10(ls counter 22 is electrically connected to the corresponding segment 36 (not shown) in the lOs counter 21.

The circumferential extent of each of the stator contacts 41 is one-twentieth of a circle or 18 and the spacing between the stator contacts is of the same dimension so that the first solenoid coil 4- in the units counter 29 is energized for ten equal time periods and (ls-energized for ten alternate equal time periods in the course of one revolution of the first shaft 3'11 in the units counter. The purpose of the contact rotor 34 and the three segments 35, 36, and 37 in the units counter 2% is to energize and de-ene ze the second coil as in the lOs counter 21 in the same manner, that is to say, ten times on and ten times oil in the course of one rotation of the second shaft 31 in the 10s counter 21.

Since the first shaft 31 in the units counter 20 rotates ten times as fast as the second shaft 33, the desired encrgization of the lOs solenoid coil for one-twentieth of a rotation of the second shaft 3?. is achieved simply by closing a circuit with the contact 34 in the units counter 24) during 186 of rotation of the first shaft 31 and the third solenoid coil lil is energized for one-twentieth the rotation of the third shaft 31 in the same way.

A feature of the counter is the use of three segments in cooperation with the rotor contact 34 in the units counter Ztl instead of a single 180 segment thus to make possible what may be termed an electrical shift of 36 when desired in the timing of the energization of the ltls solenoid coil dil relative to the rotation of the units shaft 31. For this purpose the central stator contact 36 cooperating with the rotor contact 34 has a circumferential extent of 144 and each of the two adjacent stator contacts 35 and 37 cover an additional 36 or one tenth of a revolution of the units shaft El.

During normal operation of the units counter 20 in the range of positive values of the variable that is to be computed, the stator contact 35 is electrically connected to the adjacent stator contact 36 to make up the required 180 and such electrical connection may be permanent if the computing device is to be used only for positive values of the variable. In the range of operation for negative values of the variable, however, the stator contact 37 instead of the stator contact 35 is connected with the adjacent stator contact 36 to make up the required 180, the result being an electrical shift of 36?. To make such a shift possible without the use of special moving parts within the structure of the counter assembly, a suitable external switching means (not shown) is employed.

The counter structure shown in Figure l is an assembly of individual counters in the form of standard units that are inter-changeable and are adapted to be assembled together and inter-connected to make a bank of any desired number of units to handle any desired maximum totalizing numeral. Thus the counters 2t), 21, and 22 in the bank or assembly of counters in Figures 1 and 2 are all identical in structure.

Each of the counters has a cylindrical casing that is formed with two end flanges 76. The units end of the bank of counters is covered by an end cap, generally designated $0, with an end flange 81, inwhich end cap the previously mentioned input shaft 25 is mounted by a suitable ball bearinggenerally designated 82. The opposite end of the assembly is closed by a blank cap 84 of similar configuration.

ixedly mounted on the inner end of the input shaft 25 is a rotor 85 carrying the previously mentioned rotor contact 42 for cooperation with the ten special segments or stator contacts 41. The ten special segments 41 are mounted in a stator 86 of non-conducting material in the end cap 89 surrounding the inner end of the input shaft 51.

A suitable pin 92 extending from the rotor 85 into a bore 93 in a gear 46 may serve as means to operatively connect the input shaft 25 with the units counter shaft 31, the gear 46 being fixedly mounted on the end of the shaft 31. The teeth of the gear 46 have no function in the units counter 20, but as will be apparent, such teeth are necessary in the o her counters.

The fixed internal structure inside each of the counters includes four members of cylindrical cross-sectional configuration, namely; a metal block 96 having a bearing 97 to support one end of the shaft 31; the previously mentioned stator 24 which is in the form of a cylinder of non-conducting material in which are embedded the numerous fixed stator contacts or segments of the counter; a cylindrical housing 99 for the solenoid coil 40; and, finally, a second metal block 100 in which is mounted a second bearing 101 to support the second end of the shaft 31. These four members are confined longitudinally between a pair of retaining rings 102 that seat in inner circumferential grooves 103 and the four are held in alignment against rotation by a suitable key in the form of a long pin 104 that seats in a keyway 105. The metal block 96 has a longitudinal bore 106 which has no function in the units counter 20.

The shaft 31 of each counter is slidingly mounted in its two bearings 97 and 101 for a short range of longitudinal reciprocation and when the corresponding solenoid core 40 is de-energized the shaft is in a rightward position as shown in Figure 1. The shaft is urged to its rightward position by a suitable coil spring 110 under compression between the bearing 97 and the gear 46 on the end of the shaft, the rightward shift being limited by a fixed ring 107 on the shaft moving against the shaft bearing 101. When the solenoid coil 40 is energized it magnetically attracts a conical armature 111 that is fixedly mounted on the shaft 31, thereby shifting the shaft longitudinally to the left as viewed in Figure l, the magnetic force being sufficient to overcome the resistance of the spring 110.

The second end of each shaft 31 fixedly carries the previously mentioned small gear 43 in the train of gears that operatively connects each counter with the adjacent counter of higher order. As shown in Figure 1 the small gear 43 in the units counter 20 is secured to the shaft 31 by a pin 112 and the gear 44 with which it meshes is supported by a pivot pin 113 seated in the previously mentioned bore 106 in the metal block 96 of the tens counter 21. In the particular construction shown, the small gear 45 is mounted directly on the pivot pin 113 and has a tubular extension 114 on which the gear 44 is fixedly mounted. The gear 45 meshes with the gear 46 on the shaft 31.

In accord with the primary purpose of the invention it is contemplated that the rotor 23 will be equipped with centrifugal force that tends to urge the four rotor contacts 29, 30, 32, and 34 outward. In the particular construction shown in the drawings, the rotor 23 is a body of non-conducting material that has an axial bore 118 to receive the shaft 31, the axial bore having a noncircular enlargement 119 (Figure 4) to engage a corresponding non-circular portion 120 (Figure 1) of the shaft 31. The rotor is formed with four pairs of diametrically opposite peripheral recesses 121, each pair of the recesses corresponding to one of the four rotor contacts. Each of the four rotor contacts 29, 30, 32 and 34 is carried by a corresponding circumferential leaf spring 123 that embraces the rotor 23 with the ends of the leaf spring anchored to the rotor by a radial headed pin 124. Each of the circumferential leaf springs 123 extends over one of the pairs of peripheral recesses 121 and each pair of recesses loosely houses a corresponding pair of centrifugal weights 125, each weight being connected to the corresponding leaf spring 123 by a headed pin 126.

in the course of fabricating such a construction, each leaf spring is connected to the two corresponding weights and the corresponding rotor contact to make an assembly as shown in Figure 6. In Figure 6 the rotor contact 32, for example, is mounted in the middle of a flat leaf spring 123 and the two corresponding centrifugal weights 125 are attached thereto by the previously mentioned pins 6 126. It will be noted that the leaf spring 123 has apertures 127 near its opposite ends, which are to receive the pin 124 for mounting the leaf spring on the rotor.

The manner in which the rotor contact 32 may be mounted in the center of the leaf spring 123 is illustrated in Figure 7 and 8. The rotor contact 32 is initially formed with a contact head 130, a short cylindrical neck 131 and relatively long shank 132. As shown in Figure 7 the neck 131 is inserted in an aperture 133 in the center of the leaf spring and then the metal of the neck 131 is spun or swaged into engagement with the leaf spring as shown in Figure 8.

When this assembly comprising a rotor contact, a leaf spring 123, and two centrifugal weights 125, is mounted on the rotor 23 by a headed pin 124, the leaf spring in the region of the rotor contact forms an outwardly extending bow 136, as shown in Figure 5, the bow being relatively sharp because of the weakening of the leaf spring by the central aperture 133. Thus the leaf spring 123 is inherently biased to yieldingly thrust the rotor contact outward and at the same time is yieldingly biased to tend to urge the two centrifugal weights inward in the corresponding peripheral recesses 121.

When the rotor 23 is installed inside the corresponding stator 24 the rotor contact 32 is forced radially inward from its unrestrained biased position of Figure 5 to the position shown in Figure 4, so that normally, i. e. when the rotor is stationary or is rotating at slow speed, the rotor contact exerts appreciable pressure outward against the surrounding stator. When the rotor rotates, however, centrifugal force tends to urge the two weights 125 radially outward, but any such radial outward movement of the two centrifugal weights spreads the two ends of the bowed portion 126 of the leaf spring and thereby retracts the rotor contact 32.

It is apparent that the effectiveness of centrifugal force on the two weights 125 with respect to retractive force on the corresponding rotor contact 32 will depend on the flexibility of the leaf spring 123 as Well as the mass and radial position of the two weights 125 relative to the mass and radial position of the rotor contact 32. If the two centrifugal weights 125 are relatively light in comparison to the weight of the contact 29 and the resistance to flexure of the leaf spring 123, the centrifugal effect of the two weights will "be merely to modify the outward pressure of the rotor contact against the stator under high speed conditions without actually retracting the rotor contact from the stator.

On the other hand, the centrifugal weights 125 may be of relatively high mass in comparison with the mass of the rotor contact 32 to cause the rotor contact to actually retract under high speed conditions. Preferably the weights 125 in this particular embodiment of the invention are relatively heavy to cause such positive retraction because in the normal use of the counter the circuits involved need be closed only when the counter is stationary or is operating at relatively slow speed.

It is apparent that in both instances wear on the rotor contacts and the stator structure will be reduced by the invention and that wear will be greatly reduced if the centrifugal weights are heavy enough to completely retract the rotor contact. In the present counter such reduc tion if not elimination of pressure between the rotor contacts and the stator under high speed conditions is especially important because the rotor contacts in following their broken paths move a relatively large distance with respect to the stator for each rotation of the rotor.

It will be noted that the circumferential leaf spring 123 performs several different functions. The leaf spring serves as means to movably mount the corresponding rotor contact on the rotor; it provides the normal bias for urging the rotor contact radially outward; it provides the normal bias for urging the two centrifugal weights 125 inward; it serves as means to retain the centrifugal weights on the rotor; it serves as means to operatively connect the centrifugal weights with the rotor contacts; and, finally, the leaf spring serves as means for electrically connecting the rotor contact in a circuit.

In the particular counter of the present embodiment of the invention, the two rotor contacts 29 and 32 are electrically connected together and the two rotor contacts 30 and 34 are both connected to ground. To electrically interconnect the two contacts 29 and 32 the rotor is provided with a metal strip 139 (Figure 1) interconnecting the two leaf springs 123 that correspond to the two rotor contacts 29 and 32. The interconnecting metal strip 139 is held in place by the two pins 124 of the two associated leaf springs 123. For the purpose of grounding the two rotor contacts and 34 :a longitudinal leaf spring 140 (Figures 1 and 5) interconnects the two leaf springs 123 that correspond to the two rotor contacts 30 and 34, the longitudinal leaf spring being held in place by the two corresponding headed pins 124. The longitudinal leaf spring 140 extends over the end face of the rotor into a radial groove 141 in the rotor face and presses against the shaft 31 in the manner shown to make the desired ground connection.

As may be seen in Figures 1 and 2, the rotor 85 in the end cap 80 for cooperation with the end cap stator 86 is constructed in the same manner as the rotor 23 just described. Since the rotor 85 carries the single rotor contact 42, it is provided with only a single circumferential leaf spring 123 and a corresponding single pair of weights 125. In accord with the wiring diagram in Figure 3, the circumferential leaf spring 123 carrying the rotor contact 42 is grounded to the input shaft 25 in the manner described above.

It is apparent that in a counter assembly of the construction described, the rotor 85 in the end cap 89 and the rotor 23 of the units counter 20 will operate at higher speed than the rotors of the other counters. The invention is especially useful, therefore, in minimizing contact wear at this end of an assembly of counters.

Although the now preferred embodiment of the present invention has been shown and described herein, it is to 1 be understood that the invention is not to be limited thereto, for it is susceptible to changes in form and detail within the scope of the appended claims.

I claim:

1. In a computing device of the character described having a rotor, a stator surrounding the rotor, fixed contact means on said stator and contact means on said rotor to cooperate with the fixed contact means, the combination therewith of: a leaf spring anchored to said rotor and having a radially movable portion supporting said rotor contact means, said radially movable portion being biased to urge said rotor contact means outward against said fixed contact means; and centrifugal weight means spaced'ly connected with said leaf spring to draw said biased portion inward in response to rotation of the rotor, thereby to lessen the pressural engagement of said rotor contact means with said fixed contact means.

2. A combination as set forth in claim 1 in which said weight means comprises two separate weights spaced circumferentially of the rotor on opposite sides of said rotor contact means.

3. A combination set forth in claim 2 in which said leaf spring is anchored to said rotor at a point substantially diagrammatically opposite from said rotor contact means and in which said two weights are substantially diametrically opposite each other.

4. In a computing device of the character described including a stator with fixed inner circumferential contact means, the combination therewith of: a rotor in said stator having a peripheral recess; a centrifugal weight mounted in said recess for radial movement; contact means on said rotor to cooperate with said stator contact means; a leaf spring positioned circumferentially of said rotor, said leaf spring having a first portion anchored to said rotor, a second portion supporting said rotor contact means, and a third portion extending over said recess, said third portion being connected to said weight, said leaf spring having a normal bias to urge said rotor contact means outward and to urge said weight inward whereby the rotor contact means normally extends into contact with said stator contact means when the rotor is stationary and said weight acts centrifugally on said third portion to exert a retractive force on said second portion to move said rotor contact means inwardly when said rotor rotates.

5. In a computing device of the character described including a stator with fixed inner circumferential contact means, the combination therewith of: a rotor in said stator having two diametrically opposite peripheral recesses; two centrifugal weights mounted respectively in said two recesses; contact means on said rotor between said two recesses to cooperate with said stator contact means; a leaf spring positioned circumferentially of said rotor, said leaf spring being looped around the rotor and connected thereto at a point substantially diametrically opposite from said rotor contact means, said leaf spring having a portion carrying said rotor contact means and two other portions extending over said recesses respectively and connected to said weights respectively, said leaf spring having a normal bias to urge said two weights inwardly and being normally bowed outward in the region of said contact means to normally urge said rotor contact means outward into pressure contact with said fixed contact means, whereby the rotor contact means normally extends into contact with said stator contact means when the rotor is stationary and said two weights act centrifugally to tend to spread said leaf spring and thereby exert retractive force on said rotor contact means when said rotor rotates.

6. A computing device of the character described, including a stator with fixed inner circumferential contact means, the combination therewith of: a rotor in said stator; resilient means carried by said rotor and rotatable therewith; said resilient means having one portion thereof normally biased outwardly of said rotor; a contact member mounted to said one portion and yieldably urged thereby into pressural engagement with said circumferential contact means of said stator; and centrifugal weight means carried by a second portion of said resilient means to exert outwardly directed forces on said second portion in response to rotation of said rotor, the outwardly directed forces exerted on said second portion resulting in retractive forces on said first portion, whereby said contact member is drawn inwardly of said rotor in response to rotation of the latter.

7. A combination as set forth in claim 6 in which said centrifugal weight means is adapted to exert forces on said second portion resulting in refractive forces on said first portion of a magnitude to lessen the pressural engage ment of said contact member with the contact means of said stator when the rotor operates at high speed, and at relatively higher speed to exert forces to completely disengage said contact member from said stator contact means.

8. In a computing device of the character described having a stator with fixed contact means thereon, the combination therewith of: a rotor in said stator; a resilient band circumscribing said rotor and fixed at one point thereto for rotation therewith; a contact member secured to said band and normally biased thereby into engagement with said fixed contact means of the stator; and centrifugal weight means carried by said band at a point spaced from said contact member; said centrifugal weight means being movable from a normal inner position to an outer position to exert retractive force on said band at the point of attachment of said contact member thereto in response to rotation of said rotor to overcome the bias of said band and to thereby exert retractive force on said contact member.

9. A computing device of the character described, including a stator with fixed inner circumferential contact means, the combination therewith of: a rotor of non-conrotor, the outwardly directed forces exerted on said second portion resulting in retractive forces on said first portion, whereby said contact member is drawn inwardly in response to rotation of said rotor.

References Cited in the file of this patent UNITED STATES PATENTS 1,295,206 Redmond Feb. 25, 1919 1,558,304 Smulski Oct. 20, 1925 2,620,980 Brown Dec. 9, 1952 

